I've been wondering the same thing!
And T, we miss you dearly. 
Ok, I am not a builder, so feel free to add to or correct me.
Firstly, a damp course is not a FLOOD DEFENCE!!
What it is in fact is a non-permeable membrane in your brick wall usually about a 20cms above the ground level. It can be a sort of rubber sheet put in when the wall is being built or in older houses it is injected into the wall horizontally between the bricks, where the cement is I think.
The reason for the damp course is that the brickwork is capable of drawing moisture up from below the ground in a 'capillary action' which is rather like blotting paper.(you do remember blotting paper, do you not
) So, the moisture is drawn up the brickwork, hits the dpc (wow, we are talking like real builders already
) and saves your house from having walls like those in a sauna!
dpc = damp-proof course.
